The standard way to win an endgame is to queen: to advance a pawn to the eighth rank and promote it to the game’s most powerful piece.

“Underpromotion” — turning a pawn into something other than a queen — occurs almost solely in composed studies. But it happened in the eighth round of last month’s US Open in Orlando, Fla. — and turned out to be the winning move.

Grandmaster Larry Kaufman had a commanding position after 13 . . . Bf6 on the Black side of a King’s Gambit. But White, rated Expert Paul Gallegos, found a clever resource in 15 Qc4 because after 15 . . . Bxf3 16 Rxf3 Nxd4 17 Kg2!? e2 18 Rxd4, he allowed Black to push his e-pawn to the last rank.